Conventional LED chips usually have a single active layer stack extending over the entire growth area of a substrate. For the purpose of injecting current, such an LED chip has a so-called bonding pad at the front side of the LED chip and a whole-area contact metallization is applied at the rear side of the substrate, it being endeavored to expand the current flow through the LED chip as far as possible to the entire lateral extent of the active layer stack.
As an alternative to injecting current vertically, in the case of which the active layer stack is arranged in a sandwich-like manner between two contacts, there are also chip structures in which the contact connection both of the p-type side and of the n-type side is effected from the front side of the chip. This is usually the case when the substrate for the active layer stack is electrically insulated.
Despite a high efficiency of the light generating process in the active layer of up to almost 100%, such LED chips have relatively low external efficiencies. The term internal efficiency pertains to the number of generated photons divided by the number of injected electron-hole pairs. The term external efficiency pertains to the percentage of the generated photons that actually leave the semiconductor chip. The difficulty consists in decoupling the light which is generated in the areally grown active semiconductor layers having a high refractive index into the potting material having a significantly lower refractive index. In this case, it is usually only the primary light generated at a relatively small solid angle which passes toward the outside; the rest of the light is reflected back into the semiconductor by total reflection at the boundary between the semiconductor and a surrounding casting and a large part of said light is lost there through absorption in the active layer, in the substrate, at the substrate surface and at the electrical contact elements or the bonding pad.
An electroluminescent component with improved decoupling of light is known from DE 199 11 717 A1 for example. The monolithic electroluminescent component disclosed in this document has a substrate, on which are provided a multiplicity of radiation decoupling elements arranged next to one another with respect to the main radiating direction of the component. The radiation decoupling elements, which are preferably formed in cylindrical fashion, have an active layer sequence with an emission zone with at least one electroluminescent pn junction, downstream of which are arranged a so-called current aperture layer with a current passage opening for delimiting the emission zone and a contact layer. Annular contact elements are provided on the contact layers of the cylindrical radiation decoupling elements, said contact elements being interconnected by electrically conductive webs. These annular contacts cover only that region of the top side of the radiation decoupling elements through which only little radiation, or no radiation at all, would be decoupled anyway on account of total reflection at the interface between radiation decoupling element and the surrounding medium.